Description of problem:
A bcache cacheset can't be reattached to a backing device more than once.

Version-Release number of selected component (if applicable):
kernel-3.13.6-200.fc20.x86_64

How reproducible:
Reproducible every time.

Steps to Reproduce:
1. Set up bcache (e.g.
make-bcache -B /dev/sdd
make-bcache -C /dev/sdf
ls -l /sys/fs/bcache
# Notice the uuid
echo <CACHESETUUID> > /sys/block/bcache0/bcache/attach
2. Run the following
bcachedev=bcache0
cacheset=$(basename $(realpath /sys/block/$bcachedev/bcache/cache/))
echo 1 > /sys/block/$bcachedev/bcache/detach
echo $cacheset > /sys/block/$bcachedev/bcache/attach
echo 1 > /sys/block/$bcachedev/bcache/detach
echo $cacheset > /sys/block/$bcachedev/bcache/attach

Actual results:
The following is reported in dmesg:
[   62.285074] bcache: cached_dev_detach_finish() Caching disabled for sdd
[   64.764636] ------------[ cut here ]------------
[   64.764684] WARNING: CPU: 1 PID: 839 at fs/sysfs/dir.c:486 sysfs_warn_dup+0x86/0xa0()
[   64.764739] sysfs: cannot create duplicate filename '/devices/LNXSYSTM:00/device:00/PNP0A03:00/device:08/VMBUS:00/vmbus_0_5/host3/target3:0:0/3:0:0:4/block/sdd/bcache/cache'
[   64.764845] Modules linked in: target_core_pscsi target_core_file target_core_iblock iscsi_target_mod target_core_mod iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi crct10dif_pclmul crc32_pclmul ghash_clmulni_intel microcode serio_raw snd_pcsp snd_pcm snd_page_alloc snd_timer snd hv_netvsc soundcore hv_utils i2c_piix4 hyperv_keyboard i2c_core hyperv_fb bcache hv_storvsc hid_hyperv crc32c_intel ata_generic hv_vmbus pata_acpi dm_multipath
[   64.765175] CPU: 1 PID: 839 Comm: bash Not tainted 3.13.6-200.fc20.x86_64 #1
[   64.765225] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090006  05/23/2012
[   64.765292]  0000000000000009 ffff8800f2e19c58 ffffffff8168730c ffff8800f2e19ca0
[   64.765349]  ffff8800f2e19c90 ffffffff8106d47d ffff8800f32c1000 ffff8800f32c1000
[   64.765405]  ffff88007f6d61c0 0000000000000001 0000000000000000 ffff8800f2e19cf0
[   64.765461] Call Trace:
[   64.765487]  [<ffffffff8168730c>] dump_stack+0x45/0x56
[   64.765566]  [<ffffffff8106d47d>] warn_slowpath_common+0x7d/0xa0
[   64.765614]  [<ffffffff8106d4ec>] warn_slowpath_fmt+0x4c/0x50
[   64.765657]  [<ffffffff812307d6>] sysfs_warn_dup+0x86/0xa0
[   64.765698]  [<ffffffff81230830>] sysfs_add_one+0x40/0x50
[   64.765739]  [<ffffffff812313a1>] sysfs_do_create_link_sd.isra.2+0xc1/0x1f0
[   64.765792]  [<ffffffff812314f5>] sysfs_create_link+0x25/0x50
[   64.765847]  [<ffffffffa0060f2e>] bcache_device_link+0x9e/0xf0 [bcache]
[   64.765904]  [<ffffffffa0062832>] bch_cached_dev_attach+0x212/0x450 [bcache]
[   64.765964]  [<ffffffffa00683cb>] bch_cached_dev_store+0x6db/0x770 [bcache]
[   64.766015]  [<ffffffff8122f290>] ? sysfs_write_file+0x60/0x1c0
[   64.766059]  [<ffffffff8122f358>] sysfs_write_file+0x128/0x1c0
[   64.766104]  [<ffffffff811b8b34>] vfs_write+0xb4/0x1f0
[   64.766144]  [<ffffffff811b9569>] SyS_write+0x49/0xa0
[   64.766184]  [<ffffffff816962e9>] system_call_fastpath+0x16/0x1b
[   64.766228] ---[ end trace a50797e6db46d168 ]---
[   64.766263] ------------[ cut here ]------------
[   64.766306] WARNING: CPU: 1 PID: 839 at drivers/md/bcache/super.c:689 bcache_device_link+0xbc/0xf0 [bcache]()
[   64.768089] Couldn't create device <-> cache set symlinks
[   64.768129] Modules linked in:
[   64.769803]  target_core_pscsi target_core_file target_core_iblock iscsi_target_mod target_core_mod iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi crct10dif_pclmul crc32_pclmul ghash_clmulni_intel microcode serio_raw snd_pcsp snd_pcm snd_page_alloc snd_timer snd hv_netvsc soundcore hv_utils i2c_piix4 hyperv_keyboard i2c_core hyperv_fb bcache hv_storvsc hid_hyperv crc32c_intel ata_generic hv_vmbus pata_acpi dm_multipath
[   64.778289] CPU: 1 PID: 839 Comm: bash Tainted: G        W    3.13.6-200.fc20.x86_64 #1
[   64.779984] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090006  05/23/2012
[   64.783337]  0000000000000009 ffff8800f2e19d00 ffffffff8168730c ffff8800f2e19d48
[   64.785015]  ffff8800f2e19d38 ffffffff8106d47d ffff8800f1f7008c ffff8800f1f70040
[   64.786669]  ffff88007ef00040 ffffffffa006ec98 ffff88007ef00cd0 ffff8800f2e19d98
[   64.788342] Call Trace:
[   64.789925]  [<ffffffff8168730c>] dump_stack+0x45/0x56
[   64.791488]  [<ffffffff8106d47d>] warn_slowpath_common+0x7d/0xa0
[   64.793041]  [<ffffffff8106d4ec>] warn_slowpath_fmt+0x4c/0x50
[   64.794584]  [<ffffffffa0060f4c>] bcache_device_link+0xbc/0xf0 [bcache]
[   64.796113]  [<ffffffffa0062832>] bch_cached_dev_attach+0x212/0x450 [bcache]
[   64.797677]  [<ffffffffa00683cb>] bch_cached_dev_store+0x6db/0x770 [bcache]
[   64.799199]  [<ffffffff8122f290>] ? sysfs_write_file+0x60/0x1c0
[   64.800691]  [<ffffffff8122f358>] sysfs_write_file+0x128/0x1c0
[   64.802171]  [<ffffffff811b8b34>] vfs_write+0xb4/0x1f0
[   64.803624]  [<ffffffff811b9569>] SyS_write+0x49/0xa0
[   64.805067]  [<ffffffff816962e9>] system_call_fastpath+0x16/0x1b
[   64.806522] ---[ end trace a50797e6db46d169 ]---
[   64.807980] bcache: bch_cached_dev_attach() Caching sdd as bcache0 on set ceac88d3-d7ba-421e-9060-866b47093c1a

Expected results:
No warning/error messages about sysfs nodes that can't be created.

Additional info:
I have a feeling that because the sysfs nodes aren't created properly the information returned by tools like bcache-status is stale.